The US death toll from coronavirus has eclipsed Italy's for the highest in the world at more than 19,700, as Chicago and other cities across the Mid West braced for a potential surge in victims.

The US death toll passed 19,700, while Italy reported the number of dead there had climbed to nearly 19,500.

Over the past week, the number of new deaths each day has been about three times higher on average in the US than in Italy. Deaths have risen more than 9,000 for the week in the US compared with fewer than 3,000 in Italy.

About half the deaths in the US were in the New York metropolitan area, where hospital admissions were nevertheless slowing down and other indicators suggested social distancing was "flattening the curve" of infections.

But with authorities warning that the crisis in New York is far from over, the city announced its 1.1 million-pupil school system will remain closed for the rest of the academic year.

Meanwhile, European countries used roadblocks, drones, helicopters, mounted patrols and the threat of fines to keep people from travelling over the Easter weekend, as glorious weather posed an extra test of public discipline.

"Don't do silly things," said Domenico Arcuri, Italy's special commissioner for the virus emergency. "Don't go out, continue to behave responsibly as you have done until today, use your head and your sense of responsibility."

Italian authorities set up roadblocks on main thoroughfares and along highway exits to discourage people from going on trips, and France deployed 160,000 police, including officers on horseback who patrolled beaches and parks.

The pandemic's centre of gravity has long since shifted from China to Europe and the US, which now has by far the largest number of confirmed cases, with more than half a million.

But with infections levelling off in Italy, Spain and other places on the continent, governments took tentative steps towards loosening the weeks-long shutdowns of much of public life.

Some countries are planning small first steps out of the lockdown, even as public health authorities warned the virus could come back if people are not careful enough.

Austria aims to reopen small shops on Tuesday, and Spain, with more than 16,000 dead, plans to start rolling back the strictest of its measures on Monday, when it will allow workers in some non-essential industries to return to factories and construction sites after a two-week stoppage.

Spanish authorities said they will distribute 10 million face masks at major train and subway stations in a bid to prevent a jump in infections.

Italy continued to include all non-essential manufacturing in an extension of its national lockdown until May 3, but premier Giuseppe Conte held out hope that some industry could reopen earlier if conditions permit.

Mr Arcuri said the exit from the lockdown will include increased virus testing, the deployment of a voluntary contact-tracing app and mandatory blood tests as Italy seeks to set up a system of "immunity passports".

India extended its lockdown of the nation of 1.3 billion people by two more weeks, but Iran reopened government offices and businesses outside the capital after a brief nationwide lockdown to help contain the worst outbreak in the Middle East. Businesses in Tehran will be allowed to reopen next weekend.

Globally, confirmed infections rose above 1.7 million, with more than 100,000 deaths, according to a tally by Johns Hopkins University. Close to 400,000 people have recovered.